MICROBIOLOGY OF SEWAGE 333 



are seldom twice the same. Gross differences readily apparent to the 

 senses of one versed in such matters certainly exist, and in actual results 

 it is rare to find two tanks doing exactly the same kind of work. Much 

 depends of course upon the chemical character of the sewage itself, but 

 much, that is still unexplained, must eventually be traced to the great 

 diversity of the sewage flora and the complex symbiosis as well as bac- 

 terial antagonisms that are involved in the reactions with which we 

 are dealing. 



During these reactions proteins and albumins are hydrolyzed by suc- 

 cessive stages to albumoses, peptones, amino-acids, amines, and finally 

 to ammonia, carbon dioxide, methane, hydrogen, etc. Simultaneously 

 ammonia, amines, and carbon dioxide are eliminated at each stage as 

 products. The tendency then is toward simple, soluble and gas- 

 eous side products, and hence of value in the preliminary resolution 

 of the sewage. 



The Fermentation of Cellulose. The fermentation of cellulose is, 

 next to protein hydrolysis, the most important work of the anaerobic 

 bacteria in sewage treatment. So far as is definitely known this action 

 is usually confined to anaerobic conditions. The fact that fence posts 

 decay first at the surf ace of the ground, or that wood in general decays 

 more rapidly when it is exposed to only a slight degree of moisture, than 

 when it is immersed in water is only an apparent contradiction. The 

 conditions are aerobic in both cases and aerobic bacteria would not be 

 favored by total immersion but the effect in both instances seems to be 

 due to fungus growths which are more active in the moist wood. 



The anaerobic fermentation of cellulose is that which is found typ- 

 ically in marshes and of which the chief products are carbon dioxide and 

 methane or " marsh gas." Nitrogenous food material is also requisite, 

 which accounts for the preserving property of reasonably pure water 

 upon wood. 



In the septic tank the solution of cellulose is extremely rapid, and 

 large pieces of cotton cloth or rolls of paper are completely dissolved 

 within a few months. Wood itself is more resistant and withstands the 

 action of the tank for years. This is largely due to the fact that the 

 wood molecule is much more complicated than a simple cellulose 

 molecule, and, among the conifers at least, to the further fact that 

 antiseptic intercellular substances are present. 



Chemically considered the action is hydrolytic and can be imitated 



